192 research outputs found
Solitons supported by singular spatial modulation of the Kerr nonlinearity
We introduce a setting based on the one-dimensional (1D) nonlinear
Schroedinger equation (NLSE) with the self-focusing (SF) cubic term modulated
by a singular function of the coordinate, |x|^{-a}. It may be additionally
combined with the uniform self-defocusing (SDF) nonlinear background, and with
a similar singular repulsive linear potential. The setting, which can be
implemented in optics and BEC, aims to extend the general analysis of the
existence and stability of solitons in NLSEs. Results for fundamental solitons
are obtained analytically and verified numerically. The solitons feature a
quasi-cuspon shape, with the second derivative diverging at the center, and are
stable in the entire existence range, which is 0 < a < 1. Dipole (odd) solitons
are found too. They are unstable in the infinite domain, but stable in the
semi-infinite one. In the presence of the SDF background, there are two
subfamilies of fundamental solitons, one stable and one unstable, which exist
together above a threshold value of the norm (total power of the soliton). The
system which additionally includes the singular repulsive linear potential
emulates solitons in a uniform space of the fractional dimension, 0 < D < 1. A
two-dimensional extension of the system, based on the quadratic nonlinearity,
is formulated too.Comment: Physical Review A, in pres
Machine Induced Background in the Low Luminosity Insertions of the LHC
The effect of the machine induced background is studied for the low luminosity insertions of the LHC. Estimations for the fluxes of the secondary particles, induced by the proton losses in the LHC, are presented for several running conditions of the collider. The formation of the background in the machine structure is discussed
The study of the machine-induced background and its applications at the LHC
We present the recent advances in the analysis of the machine-induced background generation and formation at the LHC. Different aspects of the study of the machine background problem at the LHC are reviewed, including the background production at the different stages of the machine operation, the role and influence on the background from the collimators in the experimental insertions and the background shielding. The potential use of the machine background for the purposes of detector testing and alignment is also discussed
How much laser power can propagate through fusion plasma?
Propagation of intense laser beams is crucial for inertial confinement
fusion, which requires precise beam control to achieve the compression and
heating necessary to ignite the fusion reaction. The National Ignition Facility
(NIF), where fusion will be attempted, is now under construction. Control of
intense beam propagation may be ruined by laser beam self-focusing. We have
identified the maximum laser beam power that can propagate through fusion
plasma without significant self-focusing and have found excellent agreement
with recent experimental data, and suggest a way to increase that maximum by
appropriate choice of plasma composition with implication for NIF designs. Our
theory also leads to the prediction of anti-correlation between beam spray and
backscatter and suggests the indirect control of backscatter through
manipulation of plasma ionization state or acoustic damping.Comment: 15 pages, 4 figures, submitted to Plasma Physics and Controlled
Fusio
Superconducting fluctuations above critical temperature in the Bi<inf>2</inf>Sr<inf>2</inf>Ca<inf>1</inf><inf>âx</inf>Y<inf>x</inf>Cu<inf>2</inf>O<inf>8</inf> single crystals
© Kazan Federal University (KFU).The superconducting fluctuations above critical temperature in the Bi2Sr2Ca1âxYxCu2O8 single crystals are studied. The boundaries of the superconducting fluctuations area are defined by the MWA measurement. The estimation of the fluctuations lifetimes is made
Microwave Electrodynamics of Electron-Doped Cuprate Superconductors
We report microwave cavity perturbation measurements of the temperature
dependence of the penetration depth, lambda(T), and conductivity, sigma(T) of
Pr_{2-x}Ce_{x}CuO_{4-delta} (PCCO) crystals, as well as parallel-plate
resonator measurements of lambda(T) in PCCO thin films. Penetration depth
measurements are also presented for a Nd_{2-x}Ce_{x}CuO_{4-delta} (NCCO)
crystal. We find that delta-lambda(T) has a power-law behavior for T<T_c/3, and
conclude that the electron-doped cuprate superconductors have nodes in the
superconducting gap. Furthermore, using the surface impedance, we have derived
the real part of the conductivity, sigma_1(T), below T_c and found a behavior
similar to that observed in hole-doped cuprates.Comment: 4 pages, 4 figures, 1 table. Submitted to Physical Review Letters
revised version: new figures, sample characteristics added to table, general
clarification give
Superfluid Flow Past an Array of Scatterers
We consider a model of nonlinear superfluid flow past a periodic array of
point-like scatterers in one dimension. An application of this model is the
determination of the critical current of a Josephson array in a regime
appropriate to a Ginzburg-Landau formulation. Here, the array consists of short
normal-metal regions, in the presence of a Hartree electron-electron
interaction, and embedded within a one-dimensional superconducting wire near
its critical temperature, . We predict the critical current to depend
linearly as , while the coefficient depends sensitively on the
sizes of the superconducting and normal-metal regions and the strength and sign
of the Hartree interaction. In the case of an attractive interaction, we find a
further feature: the critical current vanishes linearly at some temperature
less than , as well as at itself. We rule out a simple
explanation for the zero value of the critical current, at this temperature
, in terms of order parameter fluctuations at low frequencies.Comment: 23 pages, REVTEX, six eps-figures included; submitted to PR
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